Dye sensitized solar cell and dye-sensitized solar cell module

ABSTRACT

A dye-sensitized solar cell formed by layering a conductive layer; a photoelectric conversion layer in which a dye is adsorbed in a porous semiconductor layer and the layer is filled with a carrier transporting material; and a counter electrode including only a counter electrode conductive layer or including a catalyst layer and a counter electrode conductive layer on a support made of a light transmitting material,
         in which the photoelectric conversion layer is brought into contact with the counter electrode; the porous semiconductor layer forming the photoelectric conversion layer has two or more layers with different light scattering properties; and the two or more porous semiconductor layers are layered in an order of from a layer with lower light scattering property to a layer with higher light scattering property from a light receiving face side of the dye-sensitized solar cell.

TECHNICAL FIELD

The present invention relates to a dye-sensitized solar cell and adye-sensitized solar cell module.

BACKGROUND ART

As an energy source in place of fossil fuel, solar cells capable ofconverting sun light to electric power have drawn attention. Presently,some of solar cells using crystalline silicon substrates and thin filmsilicon solar cells have been used practically. However, the former hasa problem of a high production cost of the silicon substrates and thelatter has a problem that the production cost is increased since variouskinds of gases for semiconductor production and complicated productionfacilities are required. Therefore, in both solar cells, it has beentried to lower the cost per electric power output by increasing theefficiency of photoelectric conversion; however, the above-mentionedproblems still remain while being unsolved.

As a new type solar cell, there has been proposed a wet type solar cellbased on photo-induced electron transfer of a metal complex (seeJapanese Patent No. 2664194; Patent Document 1).

This wet type solar cell comprises: two glass substrates each of whichhas an electrode on a surface thereof; and a photoelectric conversionlayer which contains a photoelectric conversion material having anabsorption spectrum in a visible light region by adsorbing aphoto-sensitive dye and an electrolytic material and which is sandwichedbetween the electrodes of two glass substrates. Specifically, as shownin FIG. 9, the dye-sensitized solar cell is produced by injecting anelectrolytic solution between two glass substrates. In the drawing, areference numeral 100 denotes a first support (glass substrate); areference numeral 101 denotes a second support (glass substrate); areference numeral 102 denotes a conductive layer; a reference numeral103 denotes a sealing material; a reference numeral 104 denotes aphotoelectric conversion layer; a reference numeral 105 denotes acatalyst layer; a reference numeral 106 denotes a counter conductivelayer; and a reference numeral 107 denotes a carrier transporting layer(electrolytic solution).

When the wet type solar cell is irradiated with light, electrons aregenerated in the photoelectric conversion layer, the generated electronstransfer to the electrodes through an external electric circuit, and thetransferred electrons are conveyed to the electrodes opposed owing tothe ion in the electrolytic material and turn back to the photoelectricconversion layer. Owing to the series of the flow of the electrons,electric energy is outputted.

However, since a basic structure of the dye-sensitized solar celldescribed in Patent Document 1 is a structure that the electrolyticsolution is injected between the opposed transparent conductivefilm-bearing glass substrates, it is possible to produce a trial solarcell with a small surface area, but it is difficult to practicallyproduce a solar cell with a large surface area such as 1 m square. Thatis, if one solar cell is enlarged in the surface area, the generatedcurrent is increased proportional to the area. However, since a voltagedecrease in the plane direction of the transparent conductive film to beused for the electrode parts is increased, the inner resistance inseries of the solar cell is increased. As a result, FF (fill-factor) anda short circuit current at the time of the photoelectric conversion arelowered, resulting in a problem of decrease of the photoelectricconversion efficiency.

Further, since the dye-sensitized solar cell module is produced byforming elements between the opposed transparent conductive film-bearingglass substrates, the module has problems that the production cost isincreased and the weight is increased.

In order to solve the problems on the inner resistance in series, therehas been proposed a dye-sensitized solar cell module having a pluralityof dye-sensitized solar cells connected in series (see JapaneseUnexamined Patent Publication No. 2002-540559: Patent Document 2).

In this dye-sensitized solar cell module as shown in FIG. 10, a glasssubstrate 110 bearing a transparent conductive film (electrode) 112formed in a comb-like shape by patterning and a glass substrate 111bearing a transparent conductive film (electrode) 116 and a catalystlayer 115 formed successively in a comb-like shape by patterning arestuck to each other in a manner that an insulating layer 113 isinterposed between the glass substrates so as to form respectivedye-sensitized solar cells and also a conductive path (contact layer)118 for electrically connecting a catalyst layer 115 and the transparentconductive films 112 and 116 is arranged so as to connect neighboringdye-sensitized solar cells in series and furthermore a photoelectricconversion layer 114 and an electrolytic solution 117 are sandwichedbetween the glass substrates.

Further, a dye-sensitized solar cell module having W-type seriesconnection proposed by P. M. Sommeling et al., is described in“Development Technology of Dye-Sensitized Solar Cells”, edited by HAYASEShuji and FUJISHIMA Akira, Gijutsu Kyoiku, p. 205-217, June 2003(Non-Patent Document 1).

In this dye-sensitized solar cell module as shown in FIG. 11, a poroussemiconductor layer which is a photoelectric conversion layer 214 andplatinum which is a catalyst layer 215 are alternately formed on twoglass substrates 210 and 211 bearing transparent conductive films(electrodes) 212 and 216 formed in a comb-like shape by patterning andare stuck to each other in a state that the porous semiconductor layersand the platinum on the respective glass substrates are arranged face toface and in a manner that an insulating layer 213 of a resin, or thelike, is interposed between the substrates so as to form eachdye-sensitized solar cell and an electrolytic solution 217 is sandwichedbetween the substrates.

However, the dye-sensitized solar cell modules described in PatentDocument 2 and Non-Patent Document 1 have a configuration that a basicstructure of each dye-sensitized solar cell is formed by injecting theelectrolytic solution between the opposed transparent conductivefilm-bearing glass substrates, and therefore the problems of theproduction cost and weight still remain while being unsolved.

Accordingly, in order to solve the problems of the production cost andweight, there has been proposed a dye-sensitized solar cell modulehaving one transparent conductive film-bearing glass substrate and aplurality of dye-sensitized solar cells (sometimes referred to as“photovoltaic cells”) connected in series and arranged on the glasssubstrate (e.g., see International Publication WO 97/16838: PatentDocument 3).

In the dye-sensitized solar cell module as shown in FIG. 12, eachdye-sensitized solar cell has a structure formed by successivelylayering a porous semiconductor layer (porous titanium oxide layer) 314which is a photoelectric conversion layer, a porous insulating layer(intermediate porous insulating layer) 318, and a counter electrode 315on a transparent substrate (glass substrate) 310 bearing a transparentconductive film (electrode) 312 formed in a comb-like shape bypatterning and the dye-sensitized solar cells are arranged in a mannerthat the transparent conductive film 312 of one dye-sensitized solarcell and the counter electrode 315 of a neighboring dye-sensitized solarcell are brought into contact with each other, and thus both solar cellsare connected in series. In the drawing, a reference numeral 311 denotesa top cover for tightly sealing an insulating liquid and a referencenumeral 313 denotes an insulating layer.

Further, Japanese Unexamined Patent Publication No. 2002-367686 (PatentDocument 4) discloses a dye-sensitized solar cell module having anintegrated structure including a transparent conductive film, a poroussemiconductor layer, a porous insulating layer, and a catalyst layerformed on a transparent substrate. This technique determines a particlediameter of component particles of each of the porous semiconductorlayer, the porous insulating layer, and the catalyst layer, and thus canprevent particles of formed layers from being mixed in the porous layerseach of which is an under layer when each layer is formed.

However, the dye-sensitized solar cell modules described in PatentDocuments 3 and 4 are required to successively layer the poroussemiconductor layer, the porous insulating layer, and the catalyst layeron one transparent conductive film-bearing glass substrate and fire therespective layer after formation of the respective layers. Therefore,the processing steps are increased and the transportation resistance ofa carrier transporting material is increased due to the formation of theporous insulating layer, resulting in a problem of deterioration of theperformance of the solar cell.

In general, when a catalyst layer and a porous semiconductor layer of aphotoelectric conversion layer are brought into contact with each other,leakage, that is, electron injection from the photoelectric conversionlayer to the catalyst layer and a counter conductive layer, occurs inthe contact part. In order to prevent the leakage, it is preferable toform a Schottky barrier between the catalyst layer and the poroussemiconductor layer. Accordingly, at least the catalyst layer among thecounter constituent elements is preferable to have a lower work functionthan the conduction band energy level of the porous semiconductor layerand thus activate a redox reaction of the carrier transporting material.

As a material for forming such a catalyst layer, for example, platinum(work function: 6.35 eV) is preferable in the case of using titaniumoxide (electron affinity=conduction band energy level: 4.1 eV) for theporous semiconductor layer. However, if the porous semiconductor layerand the catalyst layer are formed using fine particles, the physicalvalues (energy levels and Schottky barrier between two type materials)of the respective materials cannot often be applied as they are. Forexample, in a decomposition step such as deodorization by utilizing aphotocatalytic function of titanium oxide, there is a technique ofincreasing the photocatalytic function of titanium oxide by supportingplatinum particles in a size of several nanometers on titanium oxidefine particles in a size of several ten nanometers and it is known wellthat electrons are shifted from titanium oxide to platinum.

Therefore, in the dye-sensitized solar cell module and dye-sensitizedsolar cell described in Patent Document 3 and 4, the porous insulatinglayer using a material with a high conduction band energy level such aszirconium oxide is formed on the porous semiconductor layer.

On the other hand, in order to make the best use of incident light tothe dye-sensitized solar cell, there is a technique of forming a poroussemiconductor layer in a layered state using fine particles with variousparticle diameters and it is confirmed that this technique can improvethe performance of the solar cell (see, Japanese Unexamined PatentPublication No. 2001-93591, Patent Document 5).

In this porous semiconductor layer as shown in FIG. 13, a conductivelayer 22, a porous semiconductor layer 23 adsorbing a dye, and acatalyst layer (not illustrated) are successively layered on a support21 in an incident light (light receiving face) side. Further, in theporous semiconductor layer 23, semiconductor particles 24 with a smallerparticle diameter and semiconductor particles 25 with a larger particlediameter are layered in this order, that is, in an order of from a layerwith lower light scattering property to a layer with higher lightscattering property, from the light receiving face side.

With respect to such a porous semiconductor layer, the light absorptionprobabilities in each layer of the porous semiconductor layers 23differ. That is, the incident light from a support 21 side issuccessively absorbed by a dye adsorbed in the porous semiconductorlayer 23 formed on the conductive layer 22 and proceeds in a catalystlayer (not illustrated) direction. Since such light absorption step iscarried out in the inside of the solar cell, the dye adsorbed on aportion of the porous semiconductor layer 23 close to the support 21most absorbs light, and as the light proceeds in the catalyst layer (notillustrated) direction, the amount of incident light is decreased moreand the photoelectric conversion per unit time is lowered more.

Patent Document 1: Japanese Patent No. 2664194

Patent Document 2: Japanese Unexamined Patent Publication No.2002-540559

Patent Document 3: International Publication WO 97/16838

Patent Document 4: Japanese Unexamined Patent Publication No.2002-367686

Patent Document 5: Japanese Unexamined Patent Publication No. 2001-93591

Non-Patent Document 1: “Development Technology of Dye-Sensitized SolarCells”, edited by HAYASE Shuji and FUJISHIMA Akira, Gijutsu Kyoiku, p.205-217, June 2003

DISCLOSURE OF THE INVENTION Problems that the Invention is to Solve

The present invention aims to provide a high performance dye-sensitizedsolar cell having an improved FF and an enhanced short-circuit currentand a dye-sensitized solar cell module using the cell at low cost.

Means for Solving the Problems

In order to solve the above-mentioned problems, the inventors of thepresent invention have made investigations while taking a layerstructure of a porous semiconductor layer for efficiently using incidentlight for photoelectric conversion, a relation of energy levels of aporous semiconductor layer material and a catalyst layer material, andan electric power generation mechanism of a dye-sensitized solar cellinto consideration and consequently have found that with respect to adye-sensitized solar cell formed by layering a conductive layer, aphotoelectric conversion layer in which a dye is adsorbed in a poroussemiconductor layer and the layer is filled with a carrier transportingmaterial, and a counter electrode including only a counter electrodeconductive layer or including a catalyst layer and a counter electrodeconductive layer on a support made of a light transmitting material, ahigh performance dye-sensitized solar cell having decreasingtransportation resistance of a carrier transporting material, animproved FF and an enhanced short-circuit current without using a porousinsulating layer, which is not required for a basic mechanism of adye-sensitized solar cell, could be obtained by employing a structureformed by bringing the photoelectric conversion layer into contact withthe counter electrode and making the porous semiconductor layer have twoor more layers with different light scattering properties and layeringtwo or more porous semiconductor layers in an order of from layers withlower light scattering property to layers with higher light scatteringproperty from a light receiving face side of the dye-sensitized solarcell, and that production steps thereof could be shortened. Thus, theinventors have accomplished the present invention.

As described above, the present invention provides A dye-sensitizedsolar cell formed by layering a conductive layer; a photoelectricconversion layer in which a dye is adsorbed in a porous semiconductorlayer and the layer is filled with a carrier transporting material; anda counter electrode including only a counter electrode conductive layeror including a catalyst layer and a counter electrode conductive layeron a support made of a light transmitting material,

in which the photoelectric conversion layer is brought into contact withthe counter electrode; the porous semiconductor layer forming thephotoelectric conversion layer has two or more layers with differentlight scattering properties; and the two or more porous semiconductorlayers are layered in an order of from a layer with lower lightscattering property to a layer with higher light scattering propertyfrom a light receiving face side of the dye-sensitized solar cell.

Further, the present invention also provides a dye-sensitized solar cellmodule including at least two dye-sensitized solar cells including theabove-mentioned dye-sensitized solar cell and connected in series.

EFFECTS OF THE INVENTION

According to the present invention, it is possible to provide a highperformance dye-sensitized solar cell having an improved FF and anenhanced short-circuit current and a dye-sensitized solar cell moduleusing the cell at low cost.

In the present invention, since at least two porous semiconductor layerswith different light scattering properties are layered in an order offrom a layer with lower light scattering property to a layer with higherlight scattering property from a light receiving face side of thedye-sensitized solar cell, incident light can efficiently be utilizedfor photoelectric conversion and a particle diameter of semiconductorparticles forming the porous semiconductor layer on an opposite side ofthe light receiving face is increased. Since the amount of the dyeadsorbed in such a porous semiconductor layer is small, the incidentlight is only absorbed and reflected by the semiconductor particles. Inthe case where the porous semiconductor layer contains titanium oxideparticles, the light absorption region is about 400 nm or shorter andthe incident light is absorbed by a carrier transporting material, inwhich redox seeds such as the titanium oxide particles of the poroussemiconductor layer in the light receiving face side and iodine aredissolved, and scarcely reaches the porous semiconductor layer on theopposite side of the light receiving face.

Accordingly, in the above-mentioned configuration, due to difference ofthe basic energy levels, no leakage occurs and photoelectric conversionis not dominantly caused in the interface of the photoelectricconversion layer and the catalyst layer, where the leakage is expectedto occur, and therefore a porous insulating layer may not be formed.However, in the case of a dye-sensitized solar cell module, thedye-sensitized solar cell of the present invention having no porousinsulating layer and a conventional dye-sensitized solar cell having aporous insulating layer may be combined.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a main part showing alayer structure of a dye-sensitized solar cell according to the presentinvention (Production Example 1).

FIG. 2 is a schematic cross-sectional view of a main part showing alayer structure of a dye-sensitized solar cell module according to thepresent invention (Production Example 2).

FIG. 3 is a schematic cross-sectional view of a main part showing alayer structure of the dye-sensitized solar cell module according to thepresent invention (Production Example 3).

FIG. 4 is a schematic cross-sectional view of a main part showing alayer structure of the dye-sensitized solar cell module according to thepresent invention (Production Example 4).

FIG. 5 is a schematic cross-sectional view of a main part explaining alayer structure of the dye-sensitized solar cell module according to thepresent invention (Production Example 4).

FIG. 6 is a schematic cross-sectional view of a main part showing alayer structure of the dye-sensitized solar cell module according to thepresent invention (Example 7).

FIG. 7 is a schematic cross-sectional view of a main part showing alayer structure of the dye-sensitized solar cell module according to thepresent invention (Example 8).

FIG. 8 is a schematic cross-sectional view of a main part showing alayer structure of the dye-sensitized solar cell module according to thepresent invention (Example 9).

FIG. 9 is a schematic cross-sectional view of a main part showing alayer structure of a conventional dye-sensitized solar cell (PatentDocument 1).

FIG. 10 is a schematic cross-sectional view of a main part showing alayer structure of a conventional dye-sensitized solar cell module(Patent Document 2).

FIG. 11 is a schematic cross-sectional view of a main part showing alayer structure of a conventional dye-sensitized solar cell module(Non-Patent Document 1).

FIG. 12 is a schematic cross-sectional view of a main part showing alayer structure of a conventional dye-sensitized solar cell module(Patent Document 3).

FIG. 13 is a schematic cross-sectional view showing a layer structure ofa porous semiconductor layer in a conventional dye-sensitized solar cell(Patent Document 5).

EXPLANATION OF REFERENCE NUMBERS

-   1, 30, 40, 50: support-   31, 41, 51: cover-   2, 32, 42, 52: conductive layer-   3, 33, 43, 53: photoelectric conversion layer filled with a carrier    transporting material-   34, 44, 54: inter-cell insulating layer-   4: carrier transporting material-   5, 35, 45, 55: catalyst layer-   6, 36, 46, 56: counter electrode conductive layer-   7: output electrode-   8: sealing material-   57: porous insulating layer-   37, 47, 58: insulating layer-   21: support-   22: conductive layer-   23: porous semiconductor layer adsorbing dye-   24: semiconductor particles with smaller particle diameter-   25: semiconductor particles with larger particle diameter-   100: first support (glass substrate)-   101: second support (glass substrate)-   102: conductive layer-   103: scaling material-   104: photoelectric conversion layer-   105: catalyst layer-   106: counter electrode conductive layer-   107: carrier transporting layer (electrolytic solution)-   110, 111 210, 211: glass substrate-   112, 116, 212, 216: transparent conductive film (electrode)-   113, 213: insulating layer-   114, 214: photoelectric conversion layer-   115, 215: catalyst layer-   117, 217: electrolytic solution-   118: conductive path (contact axial layer)-   310: transparent substrate (glass substrate)-   311: top cover for tightly sealing electrical insulating liquid-   312: transparent conductive film (electrode)-   313: insulating layer-   314: porous semiconductor layer (porous titanium oxide layer)-   315: counter electrode (counter electrode)-   318: porous insulating layer (intermediate porous insulating layer)

BEST MODES FOR CARRYING OUT THE INVENTION

A dye-sensitized solar cell (hereinafter, referred to as “solar cell”)of the present invention is formed by layering a conductive layer, aphotoelectric conversion layer in which a dye is adsorbed in a poroussemiconductor layer and the layer is filled with a carrier transportingmaterial, and a counter electrode including only a counter electrodeconductive layer or including a catalyst layer and a counter electrodeconductive layer on a support made of a light transmitting material, andcharacterized in that the photoelectric conversion layer is brought intocontact with the counter electrode and the porous semiconductor layerforming the above-mentioned photoelectric conversion layer has two ormore layers with different light scattering properties and the two ormore porous semiconductor layers are layered in an order of from a layerwith lower light scattering property to a layer with higher lightscattering property from a light receiving face side of thedye-sensitized solar cell.

Further, a dye-sensitized solar cell module (hereinafter, referred to as“module”) of the present invention comprises at least two solar cellsincluding the solar cell of the present invention and connected inseries.

Preferred embodiments of the solar cell of the present invention will bedescribed with reference to drawings. These embodiments are merelyexamples and variation embodiments can be made within the scope of thepresent invention.

FIG. 1 is a schematic cross-sectional view of a main part showing thelayer structure of the solar cell according to the present invention.

In FIG. 1, a reference numeral 1 denotes a support; a reference numeral2 denotes a conductive layer; a reference numeral 3 denotes aphotoelectric conversion layer filled with a carrier transportingmaterial; a reference numeral 4 denotes a carrier transporting material;a reference numeral 5 denotes a catalyst layer; a reference numeral 6denotes a counter electrode conductive layer; a reference numeraldenotes an output electrode; and a reference numeral 8 denotes a sealingmaterial.

(Support 1)

The support is required to have light transmitting property in theportion to be a light receiving face of a solar cell and therefore ispreferable to be made of at least a light-transmitting material andpreferably have a thickness of about 0.2 to 5 mm.

A material forming the support is not particularly limited if it isgenerally useful for solar cells and capable of achieving the effects ofthe present invention. Examples of such a material include glasssubstrates of soda glass, fused quartz glass, and crystalline quartzglass, heat resistant resin sheets such as a flexible film, and thelike.

Examples of a material composing the flexible film (hereinafter,referred to as “film”) may include, for example, tetraacetyl cellulose(TAC), poly(ethylene terephthalate) (PET), poly(phenylene sulfide)(PPS), polycarbonate (PC), polyallylate (PA), poly(ether imide) (PEI), aphenoxy resin, and Teflon (registered trademark).

In the case where other layer is formed on the support by heating, forexample, in the case where a conductive layer is formed on the supportby heating at about 250° C., Teflon (registered trademark) having heatresistant at a temperature of 250° C. or more is particularly preferableamong the film materials.

Further, a support 1 may be used when a completed solar cell is attachedto other constructions. That is, it is made easy to attach theperipheral parts of the support such as a glass substrate to othersupports by using metal processing members and screws.

(Conductive Layer 2 and Counter Electrode Conductive Layer 6)

In the case where a conductive layer 2 and a counter electrodeconductive layer 6 form a light receiving face of a solar cell, lighttransmitting property is required, and therefore, at least one of thelayers is made of a light transmitting material. However, the materialmay be a material substantially transmitting light with a wavelength towhich a sensitizing dye described later has a practically effectivesensitivity and thus a material to have transmitting property for lightin the entire wavelength range is not required.

The light transmitting material is not particularly limited if it isgenerally usable for solar cells and a material capable of achieving theeffects of the present invention. Examples of such a material mayinclude indium-tin compounded oxide (ITO), fluorine-doped tin oxide(FTO), zinc oxide (ZnO), and the like.

The conductive layer 2 and the counter electrode conductive layer 6 madeof the light transmitting materials are formed by layering a materiallayer (light transmitting conductive layer) made of a light transmittingmaterial on a support (light transmitting substrate) made of a lighttransmitting material. That is, in the case of the conductive layer 2,the light transmitting substrate and the support 1 are same.

Practically, a light transmitting conductive substrate obtained bylayering a light transmitting conductive layer of FTO on a lighttransmitting substrate (support) of soda lime float glass can beexemplified and may be used preferably in the present invention.

A method for forming the light transmitting conductive layer on thelight transmitting substrate is not particularly limited and forexample, a publicly known sputtering method, spraying method, and thelike can be exemplified.

The thickness of the light transmitting conductive layer is preferablyabout 0.02 to 5 μm and the membrane resistance is more preferable as itis lower and it is preferably 40 Ω/sq or less.

The conductive layer 2 and the counter electrode conductive layer 6 notnecessarily required to have the light transmitting property may beformed using the above-mentioned light transmitting material or a lightun-transmitting material. Examples of the light un-transmitting materialmay include metal materials such as titanium, tungsten, gold, silver,copper, aluminum, nickel and the like.

Further, a metal lead wire may be formed in the conductive layer 2 tolower the resistance.

Examples of a material of the metal lead wire may include platinum,gold, silver, copper, aluminum, nickel, titanium, and the like.

A method for forming the metal lead wire may be, for example, a methodfor forming a metal lead wire on the support 1 by a publicly knownsputtering method, vapor deposition method, or the like, and forming theconductive layer 2 on the support 1 bearing the formed metal lead wire;a method for forming the conductive layer 2 on the support 1 and formingthe metal lead wire on the conductive layer 2. In this connection, inthe case where formation of the metal lead wire leads to decrease of theincident light quantity from the light receiving face, the thickness ofthe metal lead wire is preferably set to be about 0.1 to 4 mm.

(Catalyst Layer 5)

It is preferable to form a catalyst layer 5 between a photoelectricconversion layer 3 and the counter electrode conductive layer 6. Thecombination of the catalyst layer 5 and the counter electrode conductivelayer 6 may be referred to as “counter electrode”.

The catalyst layer and the photoelectric conversion layer are broughtinto contact with each other without any gap therebetween, so that (1)the inner resistance can be lowered and a FF can be increased since thetransfer distance of a redux molecule in an electrolytic solution in thecarrier transporting layer is shorter than that in the case where thegap is present and that (2) the incident light can be efficientlyutilized and the photoelectric conversion current can be increased sincethe light absorption can be prevented by a redox molecule in anelectrolytic solution in the layer of the carrier transporting materialin the gap in the case where the layer of the carrier transportingmaterial is set nearer to the light receiving face side than thephotoelectric conversion layer 3.

In general, in order to prevent leakage in the contact part of thecatalyst layer and the porous semiconductor layer of the photoelectricconversion layer, that is, electron injection into the counter electrodefrom the photoelectric conversion layer, it is preferable to form aSchottky barrier between the catalyst layer and the porous semiconductorlayer.

Accordingly, at least the catalyst layer among the constituentcomponents of the counter electrode is preferable to have a workfunction lower than the conduction band energy level of the poroussemiconductor layer.

Further, the catalyst layer is preferable to activate the redox reactionof a carrier transporting layer which will be described later.

The material composing the catalyst layer 5 is not particularly limitedif it is commonly usable for solar cells and capable of achieving theeffects of the present invention. Examples of such a material may beplatinum (work function: 6.35 eV) and carbon (work function: 4.7 eV)such as carbon black, graphite, glass carbon, amorphous carbon, hardcarbon, soft carbon, carbon whisker, carbon nanotube, fullerene, and thelike in the case of using titanium oxide (electron affinity=conductionband energy level: 4.1 eV) for the porous semiconductor layer.

Further, in the case where the catalyst layer is closer to the lightreceiving face side than the photoelectric conversion layer, since thecatalyst layer is required to have the light transmitting property, thecatalyst layer is preferable to be thin. Although differing inaccordance with the constituent material, the thickness of the catalystlayer is 0.5 to 1000 nm and preferably 0.5 to 300 nm in the case ofusing platinum.

In the case of using platinum, the catalyst layer can be formed by, forexample, a publicly known PVC method, vapor deposition method,sputtering method, and the like and in the case of using carbon, it canbe formed by an application method such as a screen printing methodusing a paste like material obtained by dispersing carbon in a solvent.

(Photoelectric Conversion Layer 3)

The photoelectric conversion layer 3 is formed by adsorbing a dye in aporous semiconductor layer.

(Porous Semiconductor Layer)

In the present invention, the porous semiconductor layer includes atleast two layers with different light scattering properties and two ormore porous semiconductor layers are layered in an order of from a layerwith lower light scattering property to a layer with higher lightscattering property from the light receiving face side of thedye-sensitized solar cell.

The porous semiconductor layer contains a semiconductor and may havevarious morphological states such as a granular state, a film-like statehaving a large number of fine pores, and the like and preferably thefilm-like state.

The semiconductor material composing the porous semiconductor layer isnot particularly limited if it is generally usable for a photoelectricconversion material. Examples of such a material may include compoundssuch as titanium oxide, zinc oxide, tin oxide, iron oxide, niobiumoxide, cerium oxide, tungsten oxide, nickel oxide, strontium titanate,cadmium sulfide, lead sulfide, zinc sulfide, indium phosphide,copper-indium sulfide (CuInS₂), CuAlO₂, SrCu₂O₂ and their combinations.Among these, titanium oxide, zinc oxide, tin oxide, and niobium oxideare preferable and titanium oxide is particularly preferable in terms ofthe photoelectric conversion efficiency, stability, and safety. Thesesemiconductor materials may be used in the form of mixtures of two ormore of these compounds.

In the present invention, titanium oxide include various kinds oftitanium oxide in a narrow sense such as anatase type titanium oxide,rutile type titanium oxide, amorphous titanium oxide, metatitanic acid,orthotitanic acid, titanium hydroxide, hydrated titanium oxide and thelike and these compounds may be used alone or in the form of mixtures.Two type crystal systems, the anatase type and rutile type, may beformed in accordance with a production method and heat hysteresis andanatase type is common.

The above-mentioned semiconductor composing the porous semiconductorlayer is preferably a polycrystalline sintered body containing fineparticles in terms of the stability, easiness of crystal growth, andproduction cost.

The light scattering property of the porous semiconductor layer can beadjusted in accordance with the particle diameter (average particlediameter) of the semiconductor material to be used for the layerformation.

Although depending on the formation conditions of the poroussemiconductor layer, practically, the porous semiconductor layer made ofsemiconductor particles with a larger average particle diameter has highlight scattering property and scatters incident light to improve thelight trapping ratio. The porous semiconductor layer made ofsemiconductor particles with a smaller average particle diameter has lowlight scattering property and contains more adsorption points of a dyeto increase the absorption amount.

Accordingly, it is preferable that two or more porous semiconductorlayers are layered in an order of from a layer with a relatively smalleraverage particle diameter to a layer with a relatively larger averageparticle diameter from the light receiving face side of the solar cell.In the present invention, “relatively” means comparison of semiconductorparticles composing the respective layers of two or more poroussemiconductor layers forming the photoelectric conversion layer in asingle solar cell.

In terms of efficient achievement of the effects of the presentinvention, it is preferable that the porous semiconductor layer with thehighest light scattering property and having a contact with the counterelectrode is formed of semiconductor particles with an average particlediameter of 50 nm or more (preferably 50 nm or more and 600 nm or less)and other porous semiconductor layers are formed of semiconductorparticles with an average particle diameter of 5 nm or more and lessthan 50 nm (preferably 10 nm or more and 30 nm or less).

The average particle diameter of the semiconductor material is notparticularly limited if it is in the above-mentioned range proper forachieving the effects of the present invention, however in terms ofefficient utilization of the incident light for photoelectricconversion, it is preferable for the semiconductor material to have aneven average particle diameter to a certain extent just likecommercialized semiconductor material powders.

However, the porous semiconductor layer having higher light scatteringproperty, particularly the porous semiconductor layer having a contactwith the counter electrode has low mechanical strength because of thelarge average particle diameter of the semiconductor material composingthe layer and it may sometimes cause a problem in the structure of thesolar cell. In such a case, a semiconductor material with a smalleraverage particle diameter may be added at a ratio, for example, 10% byweight or less to the semiconductor material with a large averageparticle diameter to mechanically reinforce the porous semiconductorlayer.

A method for forming the film-like porous semiconductor layer on aconductive layer is not particularly limited and publicly known methodsmay be exemplified. Examples may include (1) a method of applying apaste containing semiconductor particles to a conductive layer by ascreen printing method, an ink jet method, or the like and the firingthe paste; (2) a method of forming a film on a conductive layer by a CVDmethod or a MOCVD method using desired raw material gases; (3) a methodof forming a film on a conductive layer by a PVD method, a vapordeposition method, a sputtering method, or the like using solid rawmaterials; and (4) a method of forming a film on a conductive layer by asol-gel method, a method using an electrochemical redox reaction, or thelike. Among these methods, the screen printing method using a paste isparticularly preferable since a thick porous semiconductor layer can beformed at low cost.

The thickness of the porous semiconductor layer is not particularlylimited and is preferably about 0.5 to 50 μm in terms of thephotoelectric conversion efficiency.

Particularly, in terms of efficient achievement of the effects of thepresent invention, it is preferable that the thickness of the poroussemiconductor layer with the highest light scattering property andhaving a contact with the counter electrode is 0.1 to 40 μm (preferably5 to 20 μm) and the total thickness of other porous semiconductor layersis 0.1 to 50 μm (preferably 10 to 40 μm).

In order to improve the photoelectric conversion efficiency of the solarcell, it is required to form the photoelectric conversion layer byadsorbing a more amount of a dye, which will be described later, in theporous semiconductor layer. Therefore, in the case of film-like poroussemiconductor layer, a layer with a high specific surface area ispreferable and about 10 to 200 m²/g is preferable. The specific surfacearea in this specification is a value measured by a BET adsorptionmethod.

The porous semiconductor layer includes two or more layers and in termsof the efficient achievement of the effects of the present invention, itis more preferable that the porous semiconductor layer includes 3 to 5layers. That is, a plurality of porous semiconductor layers may beformed using a plurality of particle diameters sufficient for scatteringlight and reflecting light in accordance with the absorption range ofthe dye, which will be described later.

A method for forming the porous semiconductor layer using titanium oxideas semiconductor particles will be specifically described.

First, 125 mL of titanium isopropoxide (manufactured by Kishida ChemicalCo., Ltd.) is dropwise added to 750 mL of an aqueous 0.1 M nitric acidsolution (manufactured by Kishida Chemical Co., Ltd.) to causehydrolysis and the solution is heated at 80° C. for 8 hours to obtain asol solution. Thereafter, the obtained sol solution is heated at 230° C.for 11 hours in an autoclave made of titanium to grow titanium oxideparticles, and ultrasonic dispersion is carried out for 30 minutes toprepare a colloidal solution containing titanium oxide particles with anaverage particle diameter (average primary particle diameter) of 15 nm.Next, ethanol in an amount two times as much is added to the obtainedcolloidal solution and the mixture is centrifuged at a rotation speed of5000 rpm to obtain titanium oxide particles.

In this specification, the average particle diameter is a valuecalculated from the diffraction peak of XRD (x-ray diffraction method).Practically, the average particle diameter is calculated from the halfwidth of the diffraction angle in θ/2θ measurement of XRD and Scherrer'sequation. For example, in the case of anatase type titanium oxide, thehalf width of the diffraction peak (around 2θ=25.3°) corresponding to a(101) plane may be measured.

Next, the obtained titanium oxide particles are washed and mixed with asolution obtained by dissolving ethyl cellulose and terpineol inabsolute ethanol and stirred to disperse titanium oxide particles.Thereafter, the mixed solution is heated under a vacuum condition toevaporate ethanol and obtain a titanium oxide paste. The finalcomposition is adjusted such that, for example, titanium oxide solidconcentration is 20% by weight, ethyl cellulose concentration is 10% byweight, and terpineol concentration is 64% by weight.

Examples of the solvent to be used for preparing a paste containing(suspending) semiconductor particles may include, besides theabove-mentioned solvents, glyme type solvents such as ethylene glycolmonomethyl ether; alcohol type solvents such as isopropyl alcohol; mixedsolvents such as isopropyl alcohol/toluene; water; and the like.

Next, the semiconductor particles-containing paste is applied to theconductive layer and fired by the above-mentioned method to form theporous semiconductor layer. It is required to properly adjust theconditions of drying and firing, such as temperature, time, and ambientenvironments depending on the types of a support and the semiconductorparticles to be used. Firing may be carried out, for example, at fromabout 50 to 800° C. in atmospheric air or inert gas for 10 seconds to 12hours. The drying and firing may be carried out at a constanttemperature once or at changed temperatures two or more times.

(Dye)

Examples of a dye to be adsorbed in the porous semiconductor layer andhaving a function as a photo sensitizer may include various organic dyesand metal complex dyes having absorption in various visible lightregions and/or infrared regions, and one or more kinds of these dyes mayselectively be used.

Examples of the organic dyes include azo type dyes, quinone type dyes,quinoneimine type dyes, quinacridone type dyes, squarylium type dyes,cyanine type dyes, merocyanine type dyes, triphenylmethane type dyes,xanthene type dyes, porphyrin type dyes, perylene type dyes, indigo typedyes, naphthalocyanine type dyes, and the like.

The absorbance index of an organic dye is generally high as comparedwith that of a metal complex dye having morphology of coordination bondof a molecule to a transition metal.

Examples of the metal complex dyes include those having morphology ofcoordination bond of molecules to metals such as Cu, Ni, Fe, Co, V, Sn,Si, Ti, Ge, Cr, Zn, Ru, Mg, Al, Pb, Mn, In, Mo, Y, Zr, Nb, Sb, La, W,Pt, Ta, Ir, Pd, Os, Ga, Tb, Eu, Rb, Bi, Se, As, Sc, Ag, Cd, Hf, Re, Au,Ac, Tc, Te, Rh, and the like and among these, phthalocyanine type dyesand ruthenium type dyes are preferable and ruthenium type metal complexdyes are particularly preferable.

In particular, the ruthenium type metal complex dyes represented by thefollowing formulas (1) to (3) are particularly preferable.

Further, in order to firmly adsorb a dye in the porous semiconductorlayer, the dye is preferable to have an interlocking group such as acarboxylic acid group, a carboxylic anhydride group, an alkoxy group, ahydroxyl group, a hydroxyalkyl group, a sulfonic acid group, an estergroup, a mercapto group, a phosphonyl group, and the like. Among these,a carboxylic acid group and a carboxylic anhydride group areparticularly preferable. The interlocking group provides an electricbond for making the electron transfer easy between the dye in theexcited state and the conduction band of the porous semiconductor layer.

An example of a method for adsorbing the dye in the porous semiconductorlayer may be a method involving, for example, immersing the poroussemiconductor layer formed on the conductive layer in a solutioncontaining a dye (a solution for adsorbing a dye). A solvent fordissolving a dye may be any solvent which can dissolve the dye andpractical examples may be alcohols such as ethanol; ketones such asacetone; ethers such as diethyl ether and tetrahydrofuran; nitrogencompounds such as acetonitrile; halogenated aliphatic hydrocarbons suchas chloroform; aliphatic hydrocarbons such as hexane; aromatichydrocarbons such as benzene; esters such as ethyl acetate; and water.Two or more of these solvents may be used in the form of mixtures.

The concentration of a dye in the solution may be adjusted properlydepending on the types of the dye and the solvent to be used and inorder to improve the adsorption, it is more preferable as theconcentration is higher and it may be 5×10⁻⁴ mol/L or more.

(Carrier Transporting Material 4)

In the present invention, “charge transporting layer” means a region inwhich a carrier transporting material 4 is injected and which issurrounded with either a conductive layer 2 in combination with acatalyst layer 5 or a counter electrode conductive layer 6 incombination with a sealing material 8. Accordingly, the photoelectricconversion layer 3 is filled with the carrier transporting material 4.

Such a carrier transporting material is a conductive material capable oftransporting ion and preferable materials may be, for example, a liquidelectrolyte, a solid electrolyte, a gel electrolyte, a molten salt gelelectrolyte, and the like.

The liquid electrolyte may be a liquid substance containing a redoxmolecule and is not particularly limited if it can be used generally forbatteries and solar cells. Specific examples thereof include substancescontaining a redox molecule and a solvent capable of dissolving themolecule; substances containing a redox molecule and a molten saltcapable of dissolving the molecule; and substances containing a redoxmolecule, a solvent capable of dissolving the molecule, and a moltensalt capable of dissolving the molecule; and the like.

Examples of the redox molecule may include I⁻/I₃ ⁻ type, Br²⁻/Br³⁻ type,Fe²⁺/Fe³⁺ type, quinone/hydroquinone type molecules.

Specific examples thereof may include combinations of iodine (I₂) with ametal iodine such as lithium iodide (LiI), sodium iodide (NaI),potassium iodide (KI), calcium iodide (CaI₂), and the like; combinationsof iodine with a tetraalkylammonium salt such as tetraethylammoniumiodide (TEAI), tetrapropylammonium iodide (TPAI), tetrabutylammoniumiodide (TBAI), tetrahexylammonium iodide (THAI), and the like; andcombinations of bromine with a metal bromine such as lithium bromide(LiBr), sodium bromide (NaBr), potassium bromide (KBr), calcium bromide(CaBr₂), and the like and among these, the combination of LiI and I₂ isparticularly preferable.

Examples of the solvent for the redox molecule may include carbonatecompounds such as propylene carbonate; nitrile compounds such asacetonitrile; alcohols such as ethanol; water; and non-protonic polarsubstances. Among these, carbonate compounds and nitrile compounds areparticularly preferable. Two or more kinds of these solvents may be usedin the form of a mixture.

The solid electrolyte may be a conductive material capable oftransporting electron, hole, and ion, usable as an electrolyticsubstance of solar cells and has no fluidity. Specific examples mayinclude hole transporting materials such as polycarbazole;electron-transporting materials such as tetranitrofluorenone; conductivepolymers such as polypyrrole; polymer electrolytes obtained bysolidifying liquid electrolytes with polymer compounds; p-typesemiconductor such as copper iodide and copper thiocyanide; andelectrolytes obtained by solidifying liquid electrolytes containingmolten salts by fine particles.

The gel electrolyte generally includes an electrolyte and a gellingagent.

Examples of the gelling agent may include polymer gelling agents such ascrosslinked polyacrylic resin derivatives, crosslinked polyacrylonitrilederivatives, polyalkylene oxide derivatives, silicone resins, andpolymers having a nitrogen-containing heterocyclic quaternary compoundsalt structure in the side chains.

The molten salt gel electrolyte generally includes the above-mentionedgel electrolyte and an ambient temperature type molten salt.

Examples of the ambient temperature type molten salt may includenitrogen-containing heterocyclic quaternary ammonium compound salts suchas pyridinium salts, imidazolium salts, and the like.

If necessary, an additive may be added to the above-mentionedelectrolyte.

Examples of the additive may include nitrogen-containing aromaticcompounds such as tert-butylpyridine (TBP), and imidazole salts such asdimethylpropylimidazole iodide (DMPII), methylpropylimidazole iodide(MPII), ethylmethylimidazole iodide (EMII), ethylimidazole iodide (EII),and hexylmethylimidazole iodide (HMII).

The electrolyte concentration in the electrolytic solution is preferablyin a range of 0.001 to 1.5 mol/L and more preferably in a range of 0.01to 0.7 mol/L. In the case where the catalyst layer exists in the lightreceiving face side in the module of the present invention, incidentlight reaches the porous semiconductor layer adsorbing a dye through theelectrolytic solution to excite carriers. Consequently, depending on theelectrolyte concentration to be employed in a unit cell having thecatalyst layer in the light receiving face side, the performance may bedeteriorated. Therefore, the electrolyte concentration is preferable tobe set in consideration of that point.

(Output Electrode 7)

An output electrode 7 is formed based on necessity on the counterelectrode conductive layer 6.

The constituent material of the output electrode is not particularlylimited if it is generally usable for solar cells and capable ofachieving the effects of the present invention.

(Sealing Material 8)

The sealing material 8 is important to prevent evaporation of theelectrolytic solution and penetration of the cells with water.

Further, the sealing material is also important (1) to absorb the stress(impact) of dropping object to the support and (2) to absorb sagging ofthe support for long time use.

The material composing the sealing material 8 is not particularlylimited if it is generally usable for solar cells and capable ofachieving the effects of the present invention. Such a material arepreferably silicone resins, epoxy resins, polyisobutylene type resins,hot melt resins, glass frits and two of more kinds of these materialsmay be used in the form of two or more layers. In the case where anitrile type solvent or a carbonate type solvent is used as a solventfor the redox electrolyte, silicone resins, hot melt resins (e.g.,ionomer resins), polyisobutylene type resins, and glass frits areparticularly preferable.

The patterns of the sealing material 8 can be formed by using adispenser in the case of using silicone resins, epoxy resins, or glassfrits and by forming patterned holes in a sheet-like hot melt resin inthe case of using the hot melt resins.

The module of the present invention includes at least two of solar cellsincluding the solar cell of the present invention and connected inseries. That is, at least two solar cells composing the module mayinclude at least one solar cell of the present invention among at leasttwo solar cells composing the module.

Examples

The present invention will be further described by way of ProductionExamples, Examples, and Comparative Examples; however, it is notintended that the present invention is limited to these ProductionExamples and Examples.

Production Example 1

A solar cell (unit cell) shown in FIG. 1 was produced.

FIG. 1 is a schematic cross-sectional view of a main part showing thelayer structure of a solar cell of the present invention.

In FIG. 1, a reference numeral 1 denotes a support: a reference numeral2 denotes a conductive layer: a reference numeral 3 denotes aphotoelectric conversion layer filled with a carrier transportingmaterial: a reference numeral 4 denotes a carrier transporting material:a reference numeral 5 denotes a catalyst layer: a reference numeral 6denotes a counter electrode conductive layer: a reference numeral 7denotes an output electrode: and a reference numeral 8 denotes a sealingmaterial.

A glass substrate (trade name: SnO₂ film-bearing glass, manufactured byNippon Sheet Glass Co., Ltd.) obtained by forming a conductive layer 2of a SnO₂ film on a glass support 1 was used. A commercialized titaniumoxide paste (trade name: Ti-Nanoxide T/SP, average primary particlediameter of titanium oxide: 13 nm, manufactured by Solaronix) wasapplied to the conductive layer 2 of this glass substrate by using ascreen printing apparatus (model No.: LS-150, manufactured by NewlongSeimitsu Kogyo Co., Ltd.). Next, the paste was fired at 500° C. for 40minutes in air using a firing furnace (model No.: KDF P-100,manufactured by Denken Co., Ltd.) to form a 8 μm-thick titanium oxidelayer A (a porous semiconductor layer with the lowest light scatteringproperty).

Further, using the above-mentioned screen printing apparatus, acommercialized titanium oxide paste (trade name: Ti-Nanoxide D/SP,average primary particle diameter of titanium oxide: 13 nm, manufacturedby Solaronix) was applied to the titanium oxide layer A and fired at500° C. for 40 minutes in air using the firing furnace. The applicationand firing processes were repeated three times to form a 18 μm-thicktitanium oxide layer B (a porous semiconductor layer with a middle lightscattering property).

Further, using the above-mentioned screen printing apparatus, apreviously prepared titanium oxide paste was applied to the titaniumoxide layer B and fired at 500° C. for 40 minutes in air using thefiring furnace to form a 5 μm-thick titanium oxide layer C (a poroussemiconductor layer with the highest light scattering property).

The titanium oxide paste was prepared by using anatase type titaniumoxide particles with an average primary particle diameter of 350 nm andterpineol as a solvent.

In these processes, three porous semiconductor layers were formed in anorder of from a layer with the lower light scattering property to alayer with the higher light scattering property from the conductivelayer 2.

A catalyst layer 5 was formed on the obtained porous semiconductorlayers by vapor deposition of platinum in a thickness of 50 nm using avapor deposition apparatus (model No.: EVD 500A, manufactured by ANELVAcorporation).

Next, using the above-mentioned vapor deposition apparatus, titanium ina thickness of 300 nm was vapor-deposited to form a counter electrodeconductive layer 6.

The porous semiconductor layers formed by layering the layers in theabove-mentioned manner were immersed in a previously prepared dyesolution for adsorption at room temperature for 24 hours to adsorb thedye in the porous semiconductor layers. Thereafter, the substrate waswashed with ethanol and dried at about 60° C. for about 5 minutes toform the photoelectric conversion layer 3.

The dye solution for adsorption was obtained by dissolving the dyerepresented by the above-mentioned formula (3) (trade name: Ruthenium620, manufactured by Solaronix) in a solvent mixture of acetonitrile andtert-butanol at volume ratio of 1:1 so as to be a concentration of3×10⁻⁴ mol/L.

A 0.5 mm-thick titanium sheet having an electrolytic solution injectionport was used as the output electrode 7. While the output electrode 7was stuck to the counter electrode conductive layer 6 and kept inpressurized state, a UV-curable resin (model No.: 31X-101, manufacturedby Three Bond Co., Ltd.) was applied to the surrounding of the obtainedbody using a dispenser (trade name: ULTRASAVER, manufactured by EFDcorporation). Next, UV rays were quickly radiated to cure the resin andthus form the sealing material 8 by using a UV lamp (trade name:NOVACURE, manufactured by EFD corporation).

Thereafter, utilizing the capillary effect, a previously preparedelectrolytic solution as a carrier transporting material 4 was injectedin the electrolytic solution injection port of the output electrode 7and the electrolytic solution injection port was sealed to complete asolar cell.

The electrolytic solution was obtained by dissolving 0.1 mol/L of LiI(manufactured by Aldrich Chemical Company), 0.05 mol/L of 12(manufactured by Aldrich Chemical Company), 0.5 mol/L of TBP(manufactured by Aldrich Chemical Company), and 0.6 mol/L ofdimethylpropylimidazole iodide (DMPII, manufactured by Shikoku ChemicalsCorporation) in acetonitrile (manufactured by Aldrich Chemical Company).

Production Example 2

A solar cell module shown in FIG. 2 was produced.

FIG. 2 is a schematic cross-sectional view of a main part showing alayer structure of a solar cell module of the present invention. In thedrawing, a reference numeral 30 denotes a support: a reference numeral31 denotes a cover: a reference numeral 32 denotes a conductive layer: areference numeral 33 denotes a photoelectric conversion layer filledwith a carrier transporting material: a reference numeral 34 denotes aninter-cell insulating layer: a reference numeral 35 denotes a catalystlayer: a reference numeral 36 denotes a counter electrode conductivelayer: and a reference numeral 37 denotes an insulating layer.

A glass substrate (trade name: SnO₂ film-bearing glass, manufactured byNippon Sheet Glass Co., Ltd.) obtained by forming a conductive layer 32of a SnO₂ film on a glass support 1 was used. A scribe line was formedin a prescribed site of the conductive layer 32 of the glass substrateby radiating laser beam and evaporating the SnO₂ film using a laserscribe apparatus (manufactured by Seishin Trading Co., Ltd.) comprisingYAG laser (basic wavelength: 1.06 μm).

Next, in the same manner as in Production Example 1, the poroussemiconductor layer was formed using commercialized titanium oxidepastes. Thereafter, a glass paste (trade name: glass paste, manufacturedby Noritake Co., Ltd.) was applied on the scribe lines existing in therespective neighboring porous semiconductor layers by using a screenprinting apparatus (model No.; LS-150, manufactured by Newlong SeimitsuKogyo Co., Ltd.) and dried at 100° C. for 15 minutes and then fired at500° C. for 60 minutes using a firing furnace to form the inter-cellinsulating layers 34.

Next, in the same manner as in Production Example 1, the catalyst layer35 and the counter electrode conductive layer 36 were formed.Thereafter, in the same manner as in Production Example 1, the dyerepresented by the above-mentioned formula (3) was adsorbed in theporous semiconductor layers layered in the above-mentioned manner toform the photoelectric conversion layer 33. Further, a PET (polyethyleneterephthalate) sheet as the cover 31 and an EVA (ethylene vinyl acetate)sheet as the insulating layer 37 were stuck to prescribed parts.

Thereafter, in the same manner as in Production Example 1, anelectrolytic solution was injected and the electrolytic solutioninjection port was sealed to complete a solar cell module.

Production Example 3

A solar cell module shown in FIG. 3 was produced.

FIG. 3 is a schematic cross-sectional view of a main part showing alayer structure of a solar cell module of the present invention. In thedrawing, a reference numeral 40 denotes a support: a reference numeral41 denotes a cover: a reference numeral 42 denotes a conductive layer: areference numeral 43 denotes a photoelectric conversion layer filledwith a carrier transporting material: a reference numeral 44 denotes aninter-cell insulating layer: a reference numeral 45 denotes a catalystlayer: a reference numeral 46 denotes a counter electrode conductivelayer: and a reference numeral 47 denotes an insulating layer.

A solar cell module was completed in the same manner as in ProductionExample 2, except that after the porous semiconductor layers wereformed, two rows of the inter-cell insulating layers 44 were formed anthereafter, the counter electrode conductive layer 46 was formed betweenthe inter-cell insulating layers 44 to connect neighboring solar cellsin series.

Production Example 4

A solar cell module shown in FIG. 4 was produced.

FIG. 4 is a schematic cross-sectional view of a main part showing alayer structure of a solar cell module of the present invention. In thedrawing, a reference numeral 50 denotes a support: a reference numeral51 denotes a cover: a reference numeral 52 denotes a conductive layer: areference numeral 53 denotes a photoelectric conversion layer filledwith a carrier transporting material: a reference numeral 54 denotes aninter-cell insulating layer: a reference numeral 55 denotes a catalystlayer: a reference numeral 56 denotes a counter electrode conductivelayer: a reference numeral 57 denotes a porus insulating layer: areference numeral 58 denotes an insulating layer: A denotes a cell A andB denotes a cell B.

A glass substrate (trade name: SnO₂ film-bearing glass, manufactured byNippon Sheet Glass Co., Ltd.) obtained by forming a conductive layer 52of a SnO₂ film on a glass support 50 was used. A scribe line was formedin a prescribed site of the conductive layer 52 of the glass substrateby radiating laser beam and evaporating the SnO₂ film using a laserscribe apparatus (manufactured by Seishin Trading Co., Ltd.) comprisingYAG laser (basic wavelength: 1.06 μm).

Next, a commercialized catalyst paste (Pt-catalyst T/SP, manufactured bySolaronix) was applied to the conductive layer 52 of the cell B by usinga screen printing apparatus (model No.: LS-150, manufactured by NewlongSeimitsu Kogyo Co., Ltd.). Next, the paste was fired at 500° C. for 30minutes in air using a firing furnace (model No.: KDF P-100,manufactured by Denken Co., Ltd.) to form a 1 μm-thick catalyst layer 55of the cell B.

Further, a previously prepared silicon oxide paste was applied to theconductive layer 55 of the cell B and fired at 500° C. for 60 minutes inair using the above-mentioned firing furnace to form a 5 μm-thick porousinsulating layer 57.

The silicon oxide paste was prepared by using silicon oxide particles(manufactured by C.I. Kasei Co., Ltd.) with an average primary particlediameter of 30 nm and terpineol as a solvent.

The porous insulating layer 57 may be formed by a sol-gel method otherthan the above-mentioned method. For example, an organic siliconcompound (e.g., tetramethoxysilane, tetraethoxysilane, and the like),ethanol, and hydrochloric acid are dissolved in a solvent such as purewater to produce a sol solution and further, polyethylene glycol(molecular weight about 2000) as a polymer compound is added in aconcentration of about 40% by weight to the obtained sol solution. Theobtained mixed solution was applied to the catalyst layer 55 of the cellB and dried and successively fired at 500° C. for about 30 minutes inair to form the porous insulating layer 57. The above-mentioned polymercompound has a function of improving the porosity (specific surfacearea) of the porous insulating layer and may include, for example, ethylcellulose, nitrocellulose and the like, besides polyethylene glycol.

Next, in the same manner as in Production Example 1, poroussemiconductor layers were formed using commercialized titanium oxidepastes on the conductive layer 52 of the cell A and the porousinsulating layer 57 of the cell B. Thereafter, a glass paste (tradename: glass paste, manufactured by Noritake Co., Ltd.) was applied onthe scribe lines existing in the respective neighboring poroussemiconductor layers by using a screen printing apparatus (model No.;LS-150, manufactured by Newlong Seimitsu Kogyo Co., Ltd.) and dried at100° C. for 15 minutes and then fired at 500° C. for 60 minutes using afiring furnace to form the inter-cell insulating layers 54.

Next, in the same manner as in Production Example 1, the catalyst layer55 was formed on the porous semiconductor layers of the cell A and thecounter electrode conductive layer 56 was formed on the catalyst layer55 of the cell A and the porous semiconductor layers of the cell B.Thereafter, in the same manner as in Production Example 1, the dyerepresented by the above-mentioned formula (3) was adsorbed in theporous semiconductor layers layered in the above-mentioned manner toform the photoelectric conversion layer 53. Further, a PET (polyethyleneterephthalate) sheet as the cover 51 and an EVA (ethylene vinyl acetate)sheet as the insulating layer 58 were stuck to prescribed parts.

Thereafter, in the same manner as in Production Example 1, anelectrolytic solution was injected and the electrolytic solutioninjection port was sealed to complete a solar cell module.

In this Production Example 4, to efficiently utilize the incident lightfor photoelectric conversion, the porous semiconductor layers of thecell A and cell B were layered in order of a layer with a lower lightscattering property and a layer with a higher light scattering propertyfrom the light receiving face side. In this connection, if the poroussemiconductor layer with a lower light scattering layer was directlyformed on the catalyst layer in the cell B (see FIG. 5), a problem ofleakage between the porous semiconductor layer and the catalyst layercould occur, the porous insulating layer 57 was inserted between theporous semiconductor layer and the catalyst layer.

The porous insulating layer may be formed using a material which cansubstantially transmit light with wavelength to which at least thesensitizing dye has practically effective sensitivity and does notnecessarily a material having the transmittance to light in the entirewavelength region.

Example 1

In accordance with Production Example 1, a solar cell (unit cell) shownin FIG. 1 and having a light receiving surface area of 5 mm×50 mm in thephotoelectric conversion layer filled with the carrier transportingmaterial was produced. The porous semiconductor layer having the highestlight scattering property of this solar cell contained anatase typetitanium oxide particles with an average primary particle diameter of350 nm.

A black mask having an aperture part surface area of 2.49 cm² was set onthe light receiving face of the obtained solar cell and light of anintensity of 1 kW/m² (AM 1.5 solar simulator) was radiated to the solarcell to measure the short-circuit current, open circuit voltage, FF(fill factor), and photoelectric conversion efficiency (sometimesreferred to simply as “conversion efficiency”). The results are shown inTable 1.

Example 2

A solar cell was produced in the same manner as in Example 1, exceptthat anatase type titanium oxide particles with an average primaryparticle diameter of 150 nm were used for forming the poroussemiconductor layer having contact with the catalyst layer, that is, theporous semiconductor layer with the highest light scattering propertyand the solar cell was evaluated. The results are shown in Table 1.

Example 3

A solar cell was produced in the same manner as in Example 1, exceptthat rutile type titanium oxide particles with an average primaryparticle diameter of 300 nm (manufactured by Sakai Chemical IndustryCo., Ltd.) were used for forming the porous semiconductor layer havingcontact with the catalyst layer, that is, the porous semiconductor layerwith the highest light scattering property and the solar cell wasevaluated. The results are shown in Table 1.

Example 4

A solar cell was produced in the same manner as in Example 1, exceptthat rutile type titanium oxide particles with an average primaryparticle diameter of 100 nm (manufactured by Sakai Chemical IndustryCo., Ltd.) were used for forming the porous semiconductor layer havingcontact with the catalyst layer, that is, the porous semiconductor layerwith the highest light scattering property and the solar cell wasevaluated. The results are shown in Table 1.

Example 5

A solar cell was produced in the same manner as in Example 1, exceptthat rutile type titanium oxide particles with an average primaryparticle diameter of 50 nm (manufactured by Sakai Chemical Industry Co.,Ltd.) were used for forming the porous semiconductor layer havingcontact with the catalyst layer, that is, the porous semiconductor layerwith the highest light scattering property and the solar cell wasevaluated. The results are shown in Table 1.

Example 6

A solar cell was produced in the same manner as in Example 1, exceptthat a mixture of anatase type titanium oxide particles with averageprimary particle diameters of 10 nm and 350 nm (both manufactured bySakai Chemical Industry Co., Ltd.) at a weight ratio of 1:9 was used forforming the porous semiconductor layer having contact with the catalystlayer, that is, the porous semiconductor layer with the highest lightscattering property and the solar cell was evaluated. The results areshown in Table 1.

Comparative Example 1

A solar cell was produced in the same manner as in Example 1, exceptthat zirconium oxide particles with an average primary particle diameterof 50 nm (manufactured by Sakai Chemical Industry Co., Ltd.) were usedfor forming the porous insulating layer instead of the poroussemiconductor layer having contact with the catalyst layer, that is, theporous semiconductor layer with the highest light scattering propertyand the solar cell was evaluated. The results are shown in Table 1.

Comparative Example 2

A solar cell was produced in the same manner as in Example 1, exceptthat no porous semiconductor layer having contact with the catalystlayer, that is, the porous semiconductor layer with the highest lightscattering property was formed, that is, the porous semiconductor layerwith a two-layer structure of a titanium oxide layer A and a titaniumoxide layer B as shown in Production Example 1 was employed and thesolar cell was evaluated. The results are shown in Table 1.

Comparative Example 3

A solar cell having a conventional structure in which the photoelectricconversion layer was not brought into contact with the counter electrodeas shown in FIG. 9 was produced by using the porous semiconductor layerhaving a three-layer structure of the porous semiconductor layer of thesolar cell of Example 1, that is, the porous semiconductor layer havingcontact with the catalyst layer, that is, the porous semiconductor layerwith the highest light scattering property as the porous semiconductorlayer composing the photoelectric conversion layer and the solar cellwas evaluated in the same manner as in Example 1.

In the conductive layer 102 side, a glass substrate (trade name: SnO₂film-bearing glass, manufactured by Nippon Sheet Glass Co., Ltd.)obtained by forming a conductive layer 102 of a SnO₂ film on a glasssupport 100 was used. Further, in the counter electrode conductive layer106 side, a glass substrate (trade name: SnO₂ film-bearing glass,manufactured by Nippon Sheet Glass Co., Ltd.) obtained by forming acounter electrode conductive layer 106 of a SnO₂ film on a glass support101 was used and a platinum layer with a thickness of 300 nm wasdeposited as the catalyst layer 105 by vapor deposition on the counterelectrode conductive layer 106 was used. Other than these parts, theformation conditions of the sealing material 103, the photoelectricconversion layer 104, and the charge transporting layer (electrolyticsolution) were same as described in Example 1.

TABLE 1 short-circuit Open circuit conversion Masking current voltageefficiency area (mA) (V) FF (%) (cm²) Example 1 40.0 0.680 0.670 7.322.49 Example 2 39.7 0.668 0.669 7.13 2.49 Example 3 41.2 0.675 0.6657.43 2.49 Example 4 39.8 0.672 0.690 7.41 2.49 Example 5 39.7 0.6750.685 7.37 2.49 Example 6 39.8 0.679 0.672 7.29 2.49 Comparative 39.80.669 0.650 6.95 2.49 Example 1 Comparative 31.0 0.652 0.663 5.38 2.49Example 2 Comparative 40.1 0.665 0.656 7.03 2.49 Example 3

From the results shown in Table 1, as compared with the solar cell ofComparative Example 2, the solar cells of Examples 1 to 6 were foundhaving higher short-circuit current, open circuit voltage andphotoelectric conversion efficiency.. Further, although having no porousinsulating layer, the solar cells of Examples 1 to 6 were found showingshort-circuit current and open circuit voltage at same levels as thoseof the solar cells of Comparative Examples 1 and 3.

Accordingly, it can be understood that the solar cells of Examples 1 to6 show short-circuit current and open circuit voltage at same levels asthose of the solar cells of conventional techniques although having noporous insulating layer which is formed in the conventional techniquesand due to no formation of the porous insulating layer, FF can beimproved and as a result, the solar cells of the present invention havea higher conversion efficiency than that of the solar cells ofconventional techniques just like Comparative Examples 1 to 3.

Example 7

Based on Production Example 2, a solar cell module comprising three rowsas shown in FIG. 6 and having a light receiving surface area of 5 mm×50mm of the photoelectric conversion layer filled with the carriertransporting material was produced.

FIG. 6 is a schematic cross-sectional view of a main part showing alayer structure of a solar cell module of the present invention and inthe drawing, a reference numeral 30 denotes a support: a referencenumeral 32 denotes a conductive layer: a reference numeral 33 denotesthe photoelectric conversion layer filled with the carrier transportingmaterial: a reference numeral 34 denotes an inter-cell insulating layer:a reference numeral 35 denotes a catalyst layer and a reference numeral36 denotes a counter electrode conductive layer.

Further, the size in the drawing was set as follows: A 10 mm; B 5 mm; C0.5 mm; D 1 mm; E 1 mm; F 0.5 mm; G 5.25 mm; and H 6.5 mm.

A black mask having an aperture part surface area of 9.0 cm² was set onthe light receiving face of the obtained solar module and light of anintensity of 1 kW/m² (AM 1.5 solar simulator) was radiated to the solarcell module to measure the short-circuit current, open circuit voltage,FF (fill factor), and photoelectric conversion efficiency (sometimesreferred to simply as “conversion efficiency”). The results are shown inTable 2.

Example 8

Based on Production Example 3, a solar cell module comprising three rowsas shown in FIG. 7 and having a light receiving surface area of 5 mm×50mm of the photoelectric conversion layer filled with the carriertransporting material was produced.

FIG. 7 is a schematic cross-sectional view of a main part showing alayer structure of a solar cell module of the present invention and inthe drawing, a reference numeral 30 denotes a support: a referencenumeral 32 denotes a conductive layer: a reference numeral 33 denotesthe photoelectric conversion layer filled with the carrier transportingmaterial: a reference numeral 34 denotes an inter-cell insulating layer:a reference numeral 35 denotes a catalyst layer: and a reference numeral36 denotes a counter electrode conductive layer.

Further, the size in the drawing was set as follows: A 10 mm; B 5 mm; C0.5 mm; D 11 mm; E 0.5 mm; F 5.25 mm; and G 6.5 mm.

The obtained solar cell module was evaluated in the same manner as inExample 7. The results are shown in Table 2.

Example 9

Based on Production Example 4, a solar cell module comprising four rowsas shown in FIG. 8 and having a light receiving surface area of 5 mm×50mm of the photoelectric conversion layer filled with the carriertransporting material was produced.

FIG. 8 is a schematic cross-sectional view of a main part showing alayer structure of a solar cell module of the present invention and inthe drawing, a reference numeral 50 denotes a support: a referencenumeral 52 denotes a conductive layer: a reference numeral 53 denotesthe photoelectric conversion layer filled with the carrier transportingmaterial: a reference numeral 54 denotes an inter-cell insulating layer:a reference numeral 55 denotes a catalyst layer: and a reference numeral56 denotes a counter electrode conductive layer.

Further, the size in the drawing was set as follows: A 10 mm; B 5 mm; O0.5 mm; D 5.25 mm; and E 36 mm.

The obtained solar cell module was evaluated in the same manner as inExample 7. The results are shown in Table 2.

TABLE 2 short-circuit Open circuit conversion Masking current voltageefficiency area (mA) (V) FF (%) (cm²) Example 7 39.2 2.01 0.585 5.12 9.0Example 8 40.3 2.00 0.580 5.19 9.0 Example 9 41.1 2.69 0.594 6.11 10.75

From the results shown in Table 2, the solar cell modules of Examples 7to 9 were found having conversion efficiency as high as that of thesolar cells of Examples 1 to 6.

While the present invention has been described above, the description isillustrative of the present invention and is not to be construed aslimiting the present invention and it will be appreciated that manymodifications and variants can be made. The various modifications andapplications may occur to those skilled in the art without departingfrom the true spirit and scope of the present invention as defined bythe appended claims.

1. A dye-sensitized solar cell formed by layering a conductive layer; aphotoelectric conversion layer in which a dye is adsorbed in a poroussemiconductor layer and the layer is filled with a carrier transportingmaterial; and a counter electrode including only a counter electrodeconductive layer or including a catalyst layer and a counter electrodeconductive layer on a support made of a light transmitting material, inwhich the photoelectric conversion layer is brought into contact withthe counter electrode; the porous semiconductor layer forming thephotoelectric conversion layer has two or more layers with differentlight scattering properties; and the two or more porous semiconductorlayers are layered in an order of from a layer with lower lightscattering property to a layer with higher light scattering propertyfrom a light receiving face side of the dye-sensitized solar cell.
 2. Adye-sensitized solar cell according to claim 1, wherein the two or moreporous semiconductor layers are layered in an order of from a layer witha relatively smaller average particle diameter to a layer with arelatively larger average particle diameter from the light receivingface side of the solar cell.
 3. A dye-sensitized solar cell according toclaim 1, wherein the porous semiconductor layer with the highest lightscattering property and having a contact with the counter electrode isformed of semiconductor particles with an average particle diameter of50 nm or more and other porous semiconductor layers are formed ofsemiconductor particles with an average particle diameter of 5 nm ormore and less than 50 nm.
 4. A dye-sensitized solar cell according toclaim 1, wherein the thickness of the porous semiconductor layer withthe highest light scattering property and having a contact with thecounter electrode is 0.1 to 40 μm and the total thickness of otherporous semiconductor layers is 0.1 to 50 μm.
 5. A dye-sensitized solarcell according to claim 1, wherein the porous semiconductor layerincludes 3 to 5 layers
 6. A dye-sensitized solar cell according to claim1, wherein the porous semiconductor layer is formed of titanium oxideparticles.
 7. A dye-sensitized solar cell module including at least twodye-sensitized solar cells connected in series, wherein thedye-sensitized solar cells include a dye-sensitized solar cell formed bylayering a conductive layer; a photoelectric conversion layer in which adye is adsorbed in a porous semiconductor layer and the layer is filledwith a carrier transporting material; and a counter electrode includingonly a counter electrode conductive layer or including a catalyst layerand a counter electrode conductive layer on a support made of a lighttransmitting material, in which the photoelectric conversion layer isbrought into contact with the counter electrode; the poroussemiconductor layer forming the photoelectric conversion layer has twoor more layers with different light scattering properties; and the twoor more porous semiconductor layers are layered in an order of from alayer with lower light scattering property to a layer with higher lightscattering property from a light receiving face side of thedye-sensitized solar cell.
 8. The dye-sensitized solar cell moduleaccording to claim 7, wherein the catalyst layer or the counterelectrode conductive layer of the dye-sensitized solar cell iselectrically connected with the conductive layer of the neighboringdye-sensitized solar cell.
 9. The dye-sensitized solar cell moduleaccording to claim 7, wherein the conductive layer on the support of thedye-sensitized solar cell and the catalyst layer or the counterelectrode conductive layer on the support of the neighboringdye-sensitized solar cell are each an electrically connected singlelayer.